In lithotriptor of the type which is referred to as extracorporeal, shock waves are generated outside the patient, which waves are concentrated on the lithiases by means of a focussing device. The objects is to achieve in the vicinity of the target (in order to prevent damage to the neighbouring tissues) a pressure which suffices for fragmentation or erosion of the concretion. Therefore, the apparatus must comprise a system for exactly localizing the concretions. However, it is not only necessary to know the exact location of the concretions to be destroyed, it is also useful that their displacement, if any, under the influence of the shocks applied in the course of treatment or the movements of the organs, for example during respiration or muscular contractions of the patient, can be followed.
U.S. Pat. No. 4,617,931 describes an ultrasonic pulse apparatus for destroying calculi in which, shock waves are generated by means of an ultrasonic pulse generator comprising a spherical transducer, there is also provided an auxiliary ultrasonic generator for easy localizations of the calculus. An apparatus of this type, however, has a spatial resolution which is limited to a few milimeters because of the wavelength of the ultrasonic pulses. It may, moreover, be difficult to distinguish the echoes corresponding to the calculus itself from those which are due to other biological structures neighbouring the calculus, and a comparatively long period of time may be required for performing an analysis of neighbouring slices in order to establish the plane or planes containing the calculus.
It is to be noted that lithotriptors are known which comprise an x-ray localization system whereby, using two images taken simultaneously at two different angles by means of two flouroscopy assemblies, the position of the lithiases can be established at the intersection of two straight lines corresponding to these two angles, thus also enabling the focussing of the destructive waves. An examples of such an apparatus is described in the Patent Application WO No. 85/03631.
These lithotriptors, however, have major drawbacks. If the first fluoroscopy assembly is regarded as basic equipment enabling inter alia uralogists to perform examinations and interventions by endoscopy, the use of a similar second assembly on the one hand increases the costs of the apparatus and on the other hand forces the patient to absorb a substantial amount of radiation tubes during the entire treatment or a part thereof. The use of a single fluoroscopy assembly at two succesive angles would certainly be possible, but does not enable real-time operation. Moreover, the technique used, involving one or two fluoroscopy assemblies, leads to low contrast in the image of the calculus on the one hand because of the superposition of the images of the tissues and surrounding organs and on the other hand because of the presence of numerous scattered photons. These drawbacks are avoided by the construction in accordance with the invention.
It is an object of the invention to propose an apparatus for destroying concretions which offers, at comparatively moderate costs, an image quality and a spatial resolution better than those of the prior art.